The diffusion coefficient for interdiffusion of carbon is larger in γ-iron (FCC) than in α-iron (BCC) at 900°C due to the higher atomic mobility in the face-centered cubic structure compared to the body-centered cubic structure.
The diffusion coefficients for interdiffusion of carbon in α-iron (BCC) and γ-iron (FCC) at 900°C are influenced by the crystal structures of the respective phases. In the face-centered cubic (FCC) structure of γ-iron, atoms are arranged in a more open and symmetric pattern compared to the body-centered cubic (BCC) structure of α-iron. This difference in structure results in higher atomic mobility in the FCC phase.
The increased atomic mobility facilitates easier movement of carbon atoms within the lattice, leading to a larger diffusion coefficient in γ-iron compared to α-iron. Therefore, at 900°C, the diffusion coefficient for interdiffusion of carbon is generally larger in γ-iron due to the more favorable crystal structure that allows for enhanced atomic diffusion and mobility.